The present invention relates, in general, to an apparatus for making molded articles of plastic material, in particular molded films of thermoplastic flakes, by using a slush molding process, and more particularly to a molding apparatus of a type having a mold container with an interior space for receiving plastic material and a mold container surface which can be heated and cooled in alternating sequence, and a support frame, operated for rotating about a rotation axis of, for supporting the mold container.
European Pat. No. EP-A1 0 502 378 describes a molding apparatus for making molded films from flake-like or pulverulent plastic materials by utilizing a slush molding process. The molding apparatus includes a split mold container made of a shell heated and cooled sequentially and a powder box, whereby the mold container can be rotated back and forth about two axes in perpendicular relationship and, in addition, moved in reciprocating fashion in the direction of one pivot axis in order to realize an even film thickness and a high-grade surface quality, especially when wound configurations are involved during adherence of a layer of plastic to an inner mold container wall. The mold container is supported hereby in a support frame for limited displacement in linear direction, with the support frame being held on its ends by bearings and operated for rotation about its longitudinal axis. The bearings can be selectively moved up and down by means of separately controllable hydraulic cylinders, which additionally effect a tilting movement of the bearings in unison with the mold container about a pivot axis extending perpendicular to the longitudinal axis. Such a swivel kinematics is complicated in structure and requires powerful lifting drives. In addition, there is the drawback that the swivel motion of the mold container is possible only within a limited angular range and a biaxial, fully turnable suspension of the mold container cannot be implemented at all.
It would therefore be desirable and advantageous to provide an improved apparatus for making molded articles of plastic material, which obviates prior art shortcomings and is simple in structure and which allows a support of the mold container to allow a biaxial fully rotatable configuration and reciprocation in the direction of one axis, while reducing moving masses, and yet being reliable in operation.
According to one aspect of the present invention, an apparatus for making molded articles of plastic material, in particular molded films of thermoplastic flakes, by using a slush molding process, includes a mold container having at least one interior space for receiving plastic material and a mold wall which can be heated and cooled in alternating sequence, a support frame rotatable about a rotation axis, and a combined swivel and shift arrangement disposed between the support frame and the mold container and supporting the mold container in such a manner as to effect a rotation of the mold container about a pivot axis, which is perpendicular to the rotation axis, and a reciprocating motion in the direction of the pivot axis.
The present invention resolves prior art problems by providing a suspension of the mold container by using hinged connections that allow biaxial rotatable and linear movements, involving only very simple structural features. The linear movement and rotational movements about the pivot axis are executed by the mold container only, without conjoint movements by the support frame. As a consequence, the moving masses and thus the stress on associated bearings and drives can be kept to a minimum, and an uninhibited rotational movement of the mold container about both axes can be realized.
In order to allow variation of the movement pattern in all three degrees of freedom of the mold container, the swivel drive and the linear drive for the mold container as well as the rotary drive for the support frame can be controlled independently from one another.
According to another feature of the present invention, the mold container includes two interior spaces which are separated from one another and positioned in symmetric relationship to the pivot axis. As a result, the manufacturing capacity of the apparatus can be doubled in a simple manner.